squander::density::DepolarizingOp Class Reference

Depolarizing noise channel: ρ → (1-p)ρ + p·I/2^n. More...

#include <noise_operation.h>

Inheritance diagram for squander::density::DepolarizingOp:

Public Member Functions
void	apply_to_density (const double *params, int param_count, DensityMatrix &rho) override
	Apply this operation to the density matrix. More...
std::unique_ptr< IDensityOperation >	clone () const override
	Create a deep copy of this operation. More...
	DepolarizingOp (int qbit_num, double error_rate)
	Create depolarizing noise with fixed error rate. More...
	DepolarizingOp (int qbit_num)
	Create parametric depolarizing noise (1 parameter) More...
double	get_error_rate () const
std::string	get_name () const override
	Get operation name for debugging/display. More...
int	get_parameter_num () const override
	Get number of free parameters this operation requires. More...
int	get_qbit_num () const
bool	is_parametric () const
bool	is_unitary () const override
	Check if this is a unitary operation (gate) or non-unitary (noise) More...

Private Member Functions
void	apply_depolarizing (DensityMatrix &rho, double error_rate)

Private Attributes
double	fixed_error_rate_
bool	is_parametric_
int	qbit_num_

Detailed Description

Depolarizing noise channel: ρ → (1-p)ρ + p·I/2^n.

Represents uniform noise that replaces the quantum state with the maximally mixed state with probability p. Physically models interaction with a thermal environment.

Properties:

• Purity decreases: Tr(ρ'²) < Tr(ρ²) for p > 0
• p = 0: No noise (identity channel)
• p = 1: Complete depolarization (maximally mixed output)

Can be parametric (error rate from parameter array) or fixed.

Example:

// Fixed 1% error rate
auto noise = std::unique_ptr<DepolarizingOp>(new DepolarizingOp(2, 0.01));

// Parametric (error rate from optimizer)
auto noise = std::unique_ptr<DepolarizingOp>(new DepolarizingOp(2));

Definition at line 64 of file noise_operation.h.

Constructor & Destructor Documentation

DepolarizingOp() [1/2]

squander::density::DepolarizingOp::DepolarizingOp	(	int	qbit_num,
		double	error_rate
	)

Create depolarizing noise with fixed error rate.

Parameters

qbit_num	Number of qubits the noise acts on
error_rate	Fixed depolarizing probability p ∈ [0, 1]

Definition at line 31 of file noise_operation.cpp.

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DepolarizingOp() [2/2]

squander::density::DepolarizingOp::DepolarizingOp ( int  qbit_num )

explicit

Create parametric depolarizing noise (1 parameter)

Parameters

qbit_num

Number of qubits the noise acts on

Definition at line 41 of file noise_operation.cpp.

Member Function Documentation

apply_depolarizing()

void squander::density::DepolarizingOp::apply_depolarizing ( DensityMatrix &  rho, double  error_rate  )

private

Definition at line 69 of file noise_operation.cpp.

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apply_to_density()

void squander::density::DepolarizingOp::apply_to_density ( const double *  params, int  param_count, DensityMatrix &  rho  )

overridevirtual

Apply this operation to the density matrix.

Parameters

params	Pointer to this operation's parameters (may be nullptr if param_count=0)
param_count	Number of parameters for this operation
rho	The density matrix to modify in-place

Implements squander::density::IDensityOperation.

Definition at line 48 of file noise_operation.cpp.

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clone()

std::unique_ptr< IDensityOperation > squander::density::DepolarizingOp::clone ( ) const

overridevirtual

Create a deep copy of this operation.

Returns

Unique pointer to the cloned operation

Implements squander::density::IDensityOperation.

Definition at line 101 of file noise_operation.cpp.

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get_error_rate()

double squander::density::DepolarizingOp::get_error_rate ( ) const

inline

Definition at line 89 of file noise_operation.h.

get_name()

std::string squander::density::DepolarizingOp::get_name ( ) const

inlineoverridevirtual

Get operation name for debugging/display.

Returns

Human-readable name (e.g., "H", "CNOT", "Depolarizing")

Implements squander::density::IDensityOperation.

Definition at line 83 of file noise_operation.h.

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get_parameter_num()

int squander::density::DepolarizingOp::get_parameter_num ( ) const

inlineoverridevirtual

Get number of free parameters this operation requires.

Returns

Number of parameters (0 for constant gates/fixed noise)

Implements squander::density::IDensityOperation.

Definition at line 82 of file noise_operation.h.

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get_qbit_num()

int squander::density::DepolarizingOp::get_qbit_num ( ) const

inline

Definition at line 88 of file noise_operation.h.

is_parametric()

bool squander::density::DepolarizingOp::is_parametric ( ) const

inline

Definition at line 90 of file noise_operation.h.

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is_unitary()

bool squander::density::NoiseOperation::is_unitary ( ) const

inlineoverridevirtualinherited

Check if this is a unitary operation (gate) or non-unitary (noise)

Returns

true for unitary gates, false for noise channels

Implements squander::density::IDensityOperation.

Definition at line 38 of file noise_operation.h.

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Member Data Documentation

fixed_error_rate_

double squander::density::DepolarizingOp::fixed_error_rate_

private

Definition at line 94 of file noise_operation.h.

is_parametric_

bool squander::density::DepolarizingOp::is_parametric_

private

Definition at line 95 of file noise_operation.h.

qbit_num_

int squander::density::DepolarizingOp::qbit_num_

private

Definition at line 93 of file noise_operation.h.

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The documentation for this class was generated from the following files:

• noise_operation.h
• noise_operation.cpp